The use of artificial drying processes to remove water from green wood products prior to their being impregnated with a wood preservative agent is a common practice in today's wood preserving industry. One widely employed batch drying process is the Boulton process. In this process, the green wood products to be dried are placed in a suitable treatment vessel, submerged in a coal tar based heat transfer medium and heated to an elevated temperature while gradually applying a vacuum to the vessel. The treatment of the wood products, under these conditions, is continued until such time as a predetermined amount of water inherent in the wood products, i.e., sap water, is removed therefrom.
The sap water removed from the wood products forms a waste water stream. This stream contains various coal tar based contaminants including such materials as phenol, naphthalene, and the like. These materials are present in the heat transfer medium employed in the drying process and are stripped therefrom during the operation of the process.
Generally, the concentration of these contaminants in the waste water stream exceeds the permissible limits established by federal, state, and local authorities for waters discharged into the environment. Therefore, it is necessary to first treat the waste water stream to reduce the concentration of these contaminants to at least the permissible limits before their discharge.
While many different waste water treatment systems are available for accomplishing this reduction, a most effective and relatively inexpensive system is one based on biological oxidation. However, waste treatment systems based on biological oxidation are very sensitive to "shock loading." This phenomenon occurs from sudden and drastic changes in the compositional make-up of the waste water streams being fed to the treatment system. Thus, in the biological treatment of waste water streams which can undergo sudden and drastic changes in composition large volume equipment must be employed. The use of such large volume equipment is expensive both in terms of tankage costs as well as land utilization.